Method for preventing corrosion of petroleum acid in heavy distillate oil

Abstract

The invention provides a method for preventing corrosion of petroleum acid in heavy distillate oil, and relates to the technical field of petroleum refining processing. The method comprises the following steps: adding a deacidification preservative into heavy distillate oil, raising the temperature of the oil to 140-170 DEG C, and carrying out amidation reaction to obtain an amide compound; wherein the deacidification preservative is polyethylene polyamine; and raising the temperature of the oil to 200-260 DEG C, and further carrying out cyclization dehydration reaction to obtain the imidazoline compound. According to the invention, a continuous reaction process of amidation reaction and cyclization dehydration reaction is realized through variable-temperature operation, a deacidification product is ingeniously utilized for further reaction to generate the corrosion inhibitor, and a deacidification-corrosion inhibition synergistic corrosion prevention mechanism is constructed.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum refining and processing, and in particular to a method for preventing petroleum acid corrosion in heavy distillate oil. Background Art

[0002] Petroleum acid generally refers to cyclohexane acid and other organic acids. The total amount of cyclohexane acid in petroleum acid can account for 90% or even higher proportion of petroleum acid composition. It is generally believed that cyclohexane acid corrosion usually occurs in process media with acid value greater than 0.5mgKOH / g and temperature between 220 and 400℃ and high flow rate. It often occurs in tower plates, tower walls, furnace tubes, oil transfer lines, high-temperature pipelines and other parts. The more serious corrosion areas often occur in the shell, mouth ring and impeller of the circulation pump or high-temperature feed pump, which is easy to cause circular or elliptical corrosion pits or corrosion perforations. The corrosion of local flow-through parts is sharp blade-shaped, causing damage to equipment pipelines, leakage and fire and other dangerous situations.

[0003] In view of petroleum acid corrosion, it is generally possible to prevent corrosion by deacidification, corrosion inhibition and material upgrading. For deacidification technology, a variety of deacidification technologies have been developed at home and abroad. One is to destructively remove the carboxyl groups in petroleum acid molecules, including thermal decomposition / catalytic decomposition deacidification, organic amine / quaternary alkali solution method, catalytic hydrogenation deacidification, and esterification method; the other is to separate the petroleum acid as a whole and recover the petroleum acid resources, including adsorption separation / membrane separation, alcohol ammonia method / alkali washing method, and solvent extraction.

[0004] For corrosion inhibition technology, the industry generally selects areas with more serious corrosion to add corrosion inhibitors. The polar groups in the corrosion inhibitor molecules contain unshared electrons that can form coordination bonds with empty metal orbitals to produce adsorption. At the same time, the non-polar groups in the corrosion inhibitor molecules are oriented away from the metal surface to form a hydrophobic film, isolating the contact between petroleum acid and the metal surface, and hindering the occurrence of electrochemical corrosion reactions. For material upgrades, the carbon steel commonly used in industrial equipment is generally replaced with 316L stainless steel or 317L stainless steel to improve the corrosion resistance of the equipment, but this method is relatively expensive. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preventing petroleum acid corrosion in heavy distillate oil. Only one deacidifying agent needs to be added. Through a simple and feasible temperature-changing operation mode and a reactive distillation device, two-step serial reactions are carried out online continuously. The cyclohexane acid in the distillate oil is removed through the first step of amidation reaction, and the imidazoline-type high-temperature corrosion inhibitor is formed through the second step of cyclization dehydration reaction to protect the wall metal, thereby constructing a deacidification-corrosion inhibition synergistic anti-corrosion mechanism and completing a one-dose dual-effect protective measure.

[0006] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0007] The present invention provides a method for preventing petroleum acid corrosion in heavy distillate oil, comprising the following steps:

[0008] S1. Adding a deacidification preservative to the heavy distillate oil, raising the oil temperature to 140-170° C., causing an amidation reaction to obtain an amide compound; wherein the deacidification preservative is polyethylene polyamine;

[0009] S2. Raise the oil temperature to 200-260°C to further undergo cyclization dehydration reaction to obtain imidazoline compounds.

[0010] The following is a detailed description:

[0011] Step S1: the first step of amidation deacidification reaction stage.

[0012] Add a deacidification preservative mainly composed of polyethylene polyamine to the heavy distillate oil, raise the oil temperature to 140-170°C, and use the alkaline polyethylene polyamine as a deacidification agent to react with petroleum acid to form neutral amide compounds through amidation reaction. The reaction equation is shown below, which reduces the acid value of the distillate oil and inhibits the corrosion rate of petroleum acid.

[0013]

[0014] Heavy distillate oil refers to the distillate oil extracted from the side line of the vacuum tower of the refinery, including but not limited to the fourth-line distillate oil, the third-line distillate oil and vacuum residue oil.

[0015] In some embodiments, the polyethylene polyamine is one or more of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and polyethyleneimine, more preferably diethylenetriamine.

[0016] In some embodiments, the molar ratio of the amount of the deacidification preservative added to the distillate oil to the cyclohexane acid content in the distillate oil is 1-2: 1, preferably 1.05: 1. In the synthesis process, generally increasing the amine content appropriately is conducive to the synthesis of imidazoline, and can also inhibit the occurrence of side reactions and improve the product yield.

[0017] In some embodiments, the reaction pressure of the amidation reaction is 0.5-2 MPa, and the reaction time is 0.5-3 h.

[0018] Step S2: the second cyclodehydration reaction stage.

[0019] The temperature of the distillate oil is raised to 200-260°C, and the distillate oil is passed through a reactive distillation device, so that the amide compounds obtained in the first step of the deacidification reaction are used as reactants in the second step of the reaction, and a cyclization dehydration reaction occurs at a higher temperature to generate imidazoline compounds. The reaction equation is shown below. Amide compounds accelerate the dehydration of cycloalkanes at higher temperatures to form imidazoline compounds, which can be attached to the metal surface as a corrosion inhibitor to prevent corrosion caused by contact between petroleum acid and metal.

[0020]

[0021] In some embodiments, the oil temperature is raised to 200-260° C. by a heat exchanger or a heating furnace.

[0022] In some embodiments, the reaction pressure of the cyclodehydration reaction is 0.5-2 MPa, and the reaction time is 0.5-3 h.

[0023] In some embodiments, the cyclodehydration reaction is performed by a reactive distillation apparatus.

[0024] Preferably, the reaction distillation device is a device capable of performing reaction and separation simultaneously, and the device is composed of a reactor at the bottom and a distillation tower at the middle and upper parts. The raw materials are fed from the middle part of the reaction distillation device, and enter the reactor downward to perform cyclodehydration reaction. The water in the reaction product passes upward through the distillation tower section and leaves the device from the top of the tower in the gas phase. By destroying the reversible reaction equilibrium, the reaction conversion rate is increased and the reaction rate is improved.

[0025] Technical effect:

[0026] (1) The present invention realizes the serial reaction process of amidation reaction and cyclodehydration reaction through variable temperature operation, cleverly utilizes the deacidification product to further react to generate corrosion inhibitor, constructs the deacidification-corrosion inhibition synergistic anti-corrosion mechanism, and forms protective measures from two aspects of petroleum acid concentration and corrosion contact site.

[0027] (2) The present invention only requires one additive to achieve the effect of first deacidification and then corrosion inhibition. The corrosion inhibition effect strengthens the inhibitory effect on cyclohexane acid corrosion, while reducing the demand for the deacidification effect of the distillate oil, thereby reducing the amount of deacidification agent used, reducing costs and reducing the impact on the nitrogen content of the distillate oil.

[0028] (3) The present invention can enhance the second-stage cyclodehydration reaction by means of a reactive distillation process, promote the formation of an imidazoline-type corrosion inhibitor, and further improve the corrosion inhibition effect.

[0029] The present invention has been described in detail above, but the above embodiments are only illustrative in nature and are not intended to limit the present invention. In addition, this article is not limited by any theory described in the above prior art or invention content or the following examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the infrared spectrum of the extract before desorption.

[0031] Figure 2 This is the infrared spectrum of the four-stage extract after one-stage stripping.

[0032] Figure 3 This is the infrared spectrum of the four-step extraction solution.

[0033] Figure 4 This is the infrared spectrum of standard samples of cycloalkane acids, amide compounds and imidazoline compounds. DETAILED DESCRIPTION

[0034] The present invention is further described below in conjunction with examples. It should be noted that the following examples are provided for illustrative purposes only and do not constitute a limitation on the scope of protection claimed for the present invention.

[0035] Unless otherwise specified, the raw materials, reagents, methods, etc. used in the examples are conventional raw materials, reagents, methods in the art.

[0036] The fourth-line distillate oil comes from the refinery of Sinopec Qilu Branch;

[0037] Cyclohexane acid was obtained from Sinopharm Chemical Reagent Co., Ltd.

[0038] Corrosion rate test method:

[0039] The corrosion rate was calculated by the mass change of the test piece before and after the test. The corrosion rate V was calculated according to the following formula: L :

[0040]

[0041] Where: V L is the corrosion rate, mm / a; G0 is the mass of the specimen before corrosion, g; G is the mass of the specimen after corrosion, g; S is the surface area of ​​the specimen, cm 2 ; t is the corrosion time, h; d is the density of the test piece metal, 7.86 g / cm 3 calculate.

[0042] Example 1

[0043] The experiment was carried out in a high-pressure reactor. Diethylenetriamine was added to the four-line distillate oil at a dosage of 2000ppm. The oil temperature was first raised to 160℃, and the system pressure was maintained at 1MPa. After 2 hours of heat preservation, samples were collected and solvent extraction was performed to obtain the first-stage reaction desalination and four-line extraction liquid. Then, the oil temperature in the reactor was raised to 260℃ and the reactor was operated for 30 minutes. The pressure in the reactor was maintained at a slightly positive / negative pressure to simulate the process conditions of the reaction distillation device. After the reaction, samples were collected and solvent extraction was performed to obtain the second-stage reaction desalination and four-line extraction liquid. The four-line extraction liquid before desalination (when no deacidification reaction was performed), the first-stage desalination (after the deacidification reaction), and the four-line extraction liquid after the second-stage desalination were taken for infrared spectral analysis to obtain an infrared spectrum, as shown in the figure. Figure 1-Figure 3 shown.

[0044] The specific operation of the above solvent extraction is: first, heat the raw oil or deacidified oil to 80°C and start stirring, then gradually add 95% ethanol to the oil, and the volume ratio of agent to oil is 1.5:1. Maintain the solution temperature at 80°C, keep stirring for 20 minutes, then stop heating and stirring, and let the ethanol and oil stand to separate. Then, take the upper clear liquid, heat and evaporate the ethanol solvent to obtain the cyclopentane acid or deacidified product extract. At the same time, the lower oil phase is liquid-phase extracted again, and the secondary extract is mixed with the primary extract to fully extract the cyclopentane acid or deacidified product in the oil.

[0045] Example 2

[0046] The cyclohexane acid and the reduced four-line distillate oil were mixed in a certain proportion to obtain a corrosive medium with an acid value of 7mgKOH / g. 300g was placed in an autoclave, and diethylenetriamine was added at a molar ratio of 1:1.05 to the cyclohexane acid content in the corrosive medium. The 20# carbon steel sheet was cleaned and weighed and tied to the stirring paddle. The oil temperature was raised to 160℃ at a stirring speed of 150rpm, and the system pressure was maintained at 1MPa. After 2h of heat preservation, the oil temperature in the autoclave was raised to 260℃ and operated for 30min, and the system pressure was maintained at 1MPa. After the reaction was completed, the 20# carbon steel sheet was taken out, and the surface of the test piece was cleaned and dried with petroleum ether and ethanol, and then the mass change of the test piece before and after the test was measured to calculate the corrosion rate. The corrosion rate was 0.1631mm / a.

[0047] Example 3

[0048] The cyclohexane acid and the reduced four-line distillate oil were mixed in a certain proportion to obtain a corrosive medium with an acid value of 7mgKOH / g. 300g was placed in an autoclave, and diethylenetriamine was added in a molar ratio of 1:1.05 to the cyclohexane acid content in the corrosive medium. The 20# carbon steel sheet was cleaned and weighed and tied to the stirring paddle. The oil temperature was raised to 160℃ at a stirring speed of 150rpm, and the system pressure was maintained at 1MPa. After 2h of insulation operation, the oil temperature in the autoclave was raised to 260℃ and operated for 30min. The pressure in the autoclave was maintained at a slightly positive pressure (the purpose was to remove the water generated in the deacidification reaction from the reaction system in time to promote the reaction equilibrium to move in the positive direction of deacidification) to simulate the process conditions of the reactive distillation device. After the reaction, the 20# carbon steel sheet was taken out, and the surface of the test piece was cleaned and dried with petroleum ether and ethanol, and then the mass change of the test piece before and after the test was measured to calculate the corrosion rate. The corrosion rate was 0.1272mm / a.

[0049] Comparative Example 1

[0050] The cyclohexane acid and the reduced four-line distillate oil were prepared in a certain proportion to obtain a corrosive medium with an acid value of 7mgKOH / g. 300g was placed in an autoclave, and diethylenetriamine was added at a molar ratio of 1:1.05 to the cyclohexane acid content in the corrosive medium. The 20# carbon steel sheet was cleaned and weighed and tied to the stirring paddle. The oil temperature was raised to 160°C at a stirring speed of 150rpm, and the system pressure was maintained at 1MPa. After the heat preservation operation for 2.5h, the 20# carbon steel sheet was taken out, and the surface of the test piece was cleaned and dried with petroleum ether and ethanol, and then the mass change of the test piece before and after the test was measured to calculate the corrosion rate. The corrosion rate was 0.2283mm / a.

[0051] Comparative Example 2

[0052] The cyclohexane acid and the reduced four-line distillate oil were mixed in a certain proportion to obtain a corrosive medium with an acid value of 7mgKOH / g. 300g was taken and placed in an autoclave. The 20# carbon steel sheet was cleaned and weighed and tied to the stirring paddle. The oil temperature was raised to 160℃ at a stirring speed of 150rpm, and the system pressure was maintained at 1MPa. After 2h of heat preservation, the oil temperature in the autoclave was raised to 260℃ and operated for 30min, and the system pressure was maintained at 1MPa. After the reaction was completed, the 20# carbon steel sheet was taken out, and the surface of the test piece was cleaned and dried with petroleum ether and ethanol. Then the mass change of the test piece before and after the test was measured to calculate the corrosion rate. The corrosion rate was 0.3976mm / a.

[0053] Take standard samples of cycloalkane acid, amide compounds (amide compounds obtained by the reaction of cycloalkane acid and diethylenetriamine) and imidazoline compounds (amide compounds obtained by further cyclization and dehydration) and perform infrared spectroscopy analysis to obtain infrared spectra. Figure 4 As shown, the characteristic absorption peak of the carboxyl group in the cycloalkane acid molecule is located at 1705 cm -1The characteristic absorption peak of the amide group in the amide compound molecule is located at 1650cm -1 The characteristic absorption peak of the imidazoline ring in the imidazoline compound molecule is located at 1605 cm -1 From cyclohexane acid to amide compounds and then to imidazoline compounds, the characteristic peak of carboxylic acid can be seen to move to a lower position in the infrared spectrum. Therefore, according to this rule, the reaction progress and product distribution during the deacidification of distillate oil can be evaluated. Therefore, in Example 1, Figure 2 , Figure 3 As shown, the majority of the first-stage deacidification products are amide compounds, with a small amount of imidazoline compounds generated, while the second-stage deacidification products clearly show the generation of imidazoline compounds. The results show that the imidazoline compounds generated during the second-stage deacidification reaction can effectively protect these areas by forming corrosion inhibitors, making the deacidification agent have a deacidification-corrosion inhibition synergistic anti-corrosion mechanism.

[0054] Comparative Example 2 is the corrosion process when no deacidifying agent is added, Comparative Example 1 is the corrosion process when only the first stage deacidification reaction is carried out, Example 2 is the corrosion process when a two-stage reaction is carried out, and Example 3 is the corrosion process when a two-stage reaction is carried out and the cyclization dehydration reaction is enhanced by a reactive distillation process.

[0055] From the test results, the corrosion rate of cyclohexane acid in Comparative Example 2 is 0.3976mm / a, the corrosion rate in Comparative Example 1 is 0.2283mm / a, the corrosion rate in Example 2 is 0.1631mm / a, and the corrosion rate in Example 3 is 0.1272mm / a. It can be seen that the corrosion inhibition rate is 42.58% when only the first stage deacidification reaction is carried out, the corrosion inhibition rate is 58.98% when the two-stage reaction is carried out, and the corrosion inhibition rate is 68.01% when the two-stage reaction is carried out and enhanced by the reactive distillation process. The results show that compared with the simple deacidification reaction, the measures of deacidification-corrosion inhibition synergistic corrosion protection by performing two-stage reaction through temperature-variable operation can inhibit the corrosion process to a greater extent. At the same time, the reactive distillation process can strengthen the cyclization dehydration reaction, promote the formation of imidazoline-type corrosion inhibitors, and further improve the corrosion inhibition effect.

[0056] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and essence of the claims of the present invention; and these modifications or replacements are still within the scope defined by the claims of the present invention.

Claims

1. A method for preventing petroleum acid corrosion in heavy distillate oil, characterized in that: The following steps are involved: S1. Adding a deacidification preservative to the heavy distillate oil, raising the oil temperature to 140-170° C., causing an amidation reaction to obtain an amide compound; wherein the deacidification preservative is polyethylene polyamine; S2. Raise the oil temperature to 200-260°C to further undergo cyclization dehydration reaction to obtain imidazoline compounds.

2. The method according to claim 1, characterized in that The heavy distillate oil includes one of the following: reduced fourth-line distillate oil, reduced third-line distillate oil and vacuum residue oil.

3. The method according to claim 1, characterized in that The polyethylene polyamine is one or more of diethylene triamine, triethylene tetraamine, tetraethylene pentamine and polyethylene imine, more preferably diethylene triamine.

4. The method according to claim 1, characterized in that: The molar ratio of the amount of the deacidifying preservative added to the distillate oil to the content of cyclohexane acid in the distillate oil is 1-2:

1.

5. The method according to claim 1, characterized in that The reaction pressure of the amidation reaction is 0.5-2MPa, and the reaction time is 0.5-3h.

6. The method according to claim 1, characterized in that The reaction pressure of the cyclodehydration reaction is 0.5-2MPa, and the reaction time is 0.5-3h.

7. The method according to claim 1, characterized in that The cyclodehydration reaction is carried out by a reactive distillation device.

8. The method according to claim 7, characterized in that The reaction distillation device is composed of a reactor at the bottom and a distillation tower in the middle and upper parts. The raw materials are fed from the middle part of the reaction distillation device and enter the reactor downward to carry out cyclization dehydration reaction. The water in the reaction product passes upward through the distillation tower section and leaves the device from the top of the tower in the gas phase.

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